meso-aryl-substituted subporphyrins:: Synthesis, structures, and large substituent effects on their electronic properties
meso-aryl-substituted subporphyrins:: Synthesis, structures, and large substituent effects on their electronic properties
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DOI：
10.1021/ja069324z
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发表时间：
2007-04-18
影响因子：
15
通讯作者：
Osuka, Atsuhiro
中科院分区：
文献类型：
--
作者：
Inokuma, Yasuhide;Yoon, Zin Seok;Osuka, Atsuhiro
采用吡啶-三n -吡咯基硼烷与一系列芳基醛反应，建立了两种合成介芳基取代亚卟啉的方法。一种方法是在阿德勒条件下与氯乙酸回流1,2-二氯苯进行缩合，得到1.1-3.2%的亚卟啉；另一种方法是两步反应，先用三氟乙酸在0℃下对两种底物进行初始处理，然后在回流1,2-二氯苯中进行空气氧化，得到收率高达5.6%的亚卟啉。H-1 NMR研究表明，亚卟啉中间位苯基和无位阻取代基即使在-90℃也能自由旋转，而中位2,4,6-三甲氧基苯基取代基即使在130℃也能严格禁止旋转。x射线晶体学分析表明，6个亚卟啉的结构均为锥状三吡啶大环。与卟啉类似物相比，中位苯基取代基和无位阻碍芳基取代基与亚卟啉核心的二面角较小（38.3 ~ 55.7°），而中位2,4,6-三甲氧基取代亚卟啉的二面角较大（68.7 ~ 75.7°）。介芳基取代基的这些旋转特征导致它们对亚卟啉的电子性质有很大的影响，如4-硝基苯取代的亚卟啉14e所示，根据溶剂的不同，它的吸收和荧光光谱会受到干扰。14e荧光对溶剂极性的依赖性表明其激发态具有电荷转移特性。进行了电化学和理论研究以了解其电子特性。总之，在未来的功能器件中，介芳基取代亚卟啉是很有前途的发色团。
Two synthetic methods of meso-aryl-substituted subporphyrins have been developed by means of the reaction of pyridine-tri-N-pyrrolylborane with a series of aryl aldehydes. One method relies on the condensation under Adler conditions with chloroacetic acid in refluxing 1,2-dichlorobenzene to afford subporphyrins in 1.1-3.2%, and the other is a two-step reaction consisting of the initial treatment of the two substrates with trifluoroacetic acid at 0 degrees C followed by air-oxidation in refluxing 1,2-dichlorobenzene to provide subporphyrins in up to 5.6% yield. H-1 NMR studies indicate that phenyl and sterically unhindered substituents at the meso position of subporphyrins rotate rather freely even at -90 degrees C, whereas the rotation of meso-2,4,6-trimethoxyphenyl substituents is strictly prohibited even at 130 degrees C. The structures of six subporphyins have been revealed by X-ray crystallographic analysis to be all cone-shaped tripyrrolic macrocycles. Dihedral angles of meso-phenyl and sterically unhindered aryl substituents to the subporphyrinic core are rather small (38.3-55.7 degrees) compared to those of porphyrin analogues, whereas those of meso-2,4,6-trimethoxy-substituted subporphyrins are large (68.7-75.7 degrees). These rotational features of the meso-aryl substituents lead to their large influences on the electronic properties of subporphyrins, as seen for 4-nitrophenyl-substituted subporphyrin 14e that exhibits perturbed absorption and fluorescence spectra, depending upon solvents. Large solvent-polarity dependence of the fluorescence of 14e suggests the charge-transfer character for its excited state. Electrochemical and theoretical studies are performed to understand the electronic properties. Overall, meso-aryl-substituted subporphyrins are promising chromophores in future functional devices.